The present invention relates to an arrangement for and a method of automatically controlling a differential lock in drive axles of a motor vehicle.
The European patent document EP 0 510 457 A1 discloses a control circuit for an axle differential which, in dependence on the rotary speed difference of two drive trains, activates the engagement of a coupling. If the determined rotary speed difference exceeds a predetermined slip threshold value, the engagement of coupling is performed. This control circuit has the disadvantage that the engagement of the coupling is performed in dependence on the condition of two wheels, so that an exchange of the condition of two wheels is performed, and therefore an exchange action of the two wheels with one another during the determination of the control signal is to be considered. Moreover, for example with mechanical claw couplings the disengagement of the coupling is possible only when the transmitted torque exceeds a predetermined threshold value.
The German patent document DE 44 27 040 A1 discloses an arrangement for automatic controlling differential lock, in which the action on the lock coupling is performed in dependence on slip sum signals. A slip sum signal are formed by integration of rotary speed differences between two different wheels of the motor vehicle, for example by integration of the rotary speed difference of the both rear wheels (transverse slip) or the driven front axle and the driven rear axle (longitudinal slip). When the slip sum signal exceeds a predetermined threshold value, the activation of the actuator is performed, so that the lock coupling is engaged. The disadvantage of this known arrangement is that by the integration of the rotary speed differences, the arrangement respond only after a predetermined time interval. This is a result of the inertia of the selected integral computation type. Furthermore, for engagement of the lock coupling it is necessary to provide a spring with a fixed predetermined spring force, so that after exceeding of the applied torque under a predetermined torque value, the lock coupling is disengaged.